It was the kind of smile that made you want to smash his face in. Certainly the kind of smile that made César Sánchez want to smash his face in. Under the nose of the referee. In front of 55,000 people. And live on TV. A smug grin, a thumbs up, a glint in the eye. A yeah mate, what's the score? A talk to the hand cos the face ain't listening. A "ha-ha" from Nelson Muntz. A sly smirk, followed by the clincher: a wink. Why you little … Let me at him, let me at him, I'll pulverise him! As if it wasn't bad enough that Kun Agüero had done what he'd done, he'd done it when he'd done it and he'd reacted to doing it by laughing about doing it. It was time to do him.

The time was half-time, 45 minutes through Atlético Madrid versus Valencia, week 36 in La Liga. More than a game; not just a partido, a partidazo. A "final". A sell-out. A full house. A rocking Vicente Calderón. One of the stadium's "great nights", said coach Abel Resino. The match that would decide the future of two of Spain's biggest clubs. With Barcelona proclaimed champions, Real Madrid safe in second and Sevilla five points clear in third, it was a battle for the final Champions League place – one that, gripped by debt, threatened by the departure of their best players, both clubs desperately needed. Separated by a solitary point, the winner would take fourth ahead of the loser and Villarreal with just two games to go.

"Eight months, 3,150 minutes of football, 137 goals, countless institutional crises, some horrendous disappointments and a handful of happy moments later," said AS, "Valencia and Atlético come face to face with their whole season at stake." "This game," insisted Valencia centre-back Raúl Albiol, "decides everything." And what decided this game was a first-half penalty, scored by Diego Forlán. It finished 1–0. And as El Mundo Deportivo's online version had it – handily and instantly translated to save this column its normal hatchet job while it nips downstairs and pops on the kettle – "the Uruguayan decided from the point before the fateful Ché and places the mattress quarts."

In other words, Forlán's shot from the penalty spot clinched the match against Valencia – nicknamed the Chés – and took Atlético Madrid – nicknamed the mattress makers – into fourth. In other words, Sergio El Kun Agüero's dive took Atlético to a Champions League place. After all, it was Aguero's dive that got them the penalty in the first place.

One of the great Spanish sporting euphemisms is to "provoke" free-kicks and yellow cards, penalties and red ones. The most skilled agent provocateurs can be worth a fortune; Agüero is worth his father-in-law's weight in gold. Fifteen minutes before half-time, he dashed into the penalty area and beyond César, waited for the keeper to go down and threw himself to the turf, kicking his legs out behind him, seeking an arm, a knee, a belly, any contact. There was none but referee Mejuto González still gave it – earning him, not Agüero, the reprobation of the media (which, let's face it, is exactly the problem). Forlán sent the ball into the corner, Atlético virtually into the Champions League and Valencia into trouble.

Valencia spent six of the first eight weeks at the top of the table. But two months without being paid, an ageing squad and countless injuries saw them collapse, the chances of clinching a Champions League place gone as they failed to win in 10. They were threatened with the sack, accused of not pulling their weight and told that they were for hire, footballers available for weddings, bar mitzvahs and children's parties. They were told they had no future and a bleak present. Yet still they recovered to win seven and draw one (against Barcelona) in nine, suddenly resurrecting their chances of a top-four finish; suddenly resurrecting their chances of institutional survival. And now Kun had snatched it away again.

No wonder César confronted him, bitterly furnishing his first name with a stray "T". No wonder he bawled at him. And no wonder he had to be restrained, and pushed away down the tunnel when Kun grinned that grin and winked that wink. Agüero might have responded with a classic "Who me?" when one touchline reporter informed him after the game that replays showed there had been no contact in the move, but he replied, "No? really?" before bumbling, "Erm, well, I, er, you know, erm …". Here was the proof that his cheek was bare-faced. Here was the proof, as César was still keen to insist at the final whistle, that Valencia had been cheated.

Only, they hadn't. Well, they had. But not really. Because if Agüero's cheating "provoked" the penalty, justice was done. César might have been doing his nut at the end of the game, but few of his team-mates were venting their spleen – least of all Albiol, who had his removed after a car crash three years back. Because Kun, quickly becoming the boy who cried wolf, should quite probably have won another penalty and Atlético should certainly have had more goals; because César didn't limit himself to trying to beat up Agüero, he also beat away almost a dozen shots; and because while, without the evil machinations of Carlos Marchena and the creativity of David Silva, Valencia were poor, Atlético were worthy of their win.

On the biggest night of the season, the game that would make them or break them, Atlético were made. Not just pretty good going forward (in fact, you could argue that not even good going forward considering how many chances went begging). But, unusually, impressive at the back too. They even had a bit of a midfield. "I have no complaints whatsoever," insisted Valencia coach Unai Emery. "There is no question that Atlético were the better side." Nor is there any question that they find themselves well placed for an immediate return to the Champions League having taken 10 years to get there before, inventing a million comic ways of blowing it, each more improbable than the last. With two games remaining, against Athletic Bilbao and Almería, Atlético are fourth on 61 points – two ahead of Valencia and Villarreal, who face each other next week. "It's in our hands," beamed president Enrique Cerezo. And what better hands to be in, eh?

Talking Points

• It was a brilliant header. Diving in, Málaga's Helder Rosario turned his neck and guided it past the keeper and into the net. There was just one problem: the net was his own. Not that Sporting Gijón cared. Helder's own goal – one of three headers scored by centre-backs, all of them racking up their first of the season – gave them a 2–1 win and dragged them out of the relegation zone thanks to their head-to-head record with Osasuna. And next up for Osasuna it's Madrid and Barcelona. Mind you, that might not be a bad thing …

• Julian Faubert was asleep on the Real Madrid bench as they lost 3–2 to Villarreal on Saturday night. He didn't miss much. Not from his team anyway. The only surprise was that they scored twice in a match that they were never in. Higuaín was on the bench with him for the first half. And Raúl got one out of three in Marca – the same as Lassana Diarra. Explain that. Madrid have given up completely.

• Barcelona sent a B team out to face Real Mallorca after they became champions on Saturday night thanks to Real Madrid's 3–2 defeat at Villarreal. Which is why no one will be worried about them losing 2–1. They might be worried about Samuel Eto'o's recent tendency to miss chance after chance, though, what with Rome to come and that.

• Getafe are not out of danger yet. Espanyol, Racing and Betis, all of whom won, are. Meanwhile, Numancia still have half a chance of survival. But it is only half.

• A note to the Madrid media: the team that plays at Old Trafford is called Manchester United, not Cristiano Ronaldo.